Evaluation of High-Rate Real Time GPS Processing at USGS Pasadena

Recent advances in hardware, telemetry, and processing software make possible real-time geodetic monitoring, including monitoring of fault-crossing lifelines, increased integration of geodetic and seismic networks, and improved geodetic response to large earthquakes. USGS Pasadena operates 97 permanent continuously operating GPS stations in southern California. To further the earthquake-response mission of USGS, these stations are in heavily populated urban areas and along the southern San Andreas fault. With support from city and county land surveyors, and the USGS MultiHazards Demonstration Project, USGS Pasadena has been upgrading its stations to real-time (1 second sampling interval), and broadcasting RTCM streams, for several years. USGS Pasadena currently operates 30 stations in real time, recently co-located GPS at four new or upgraded seismic stations along the southern San Andreas fault, and anticipates upgrading many more in the next year or two. Testing of real-time processing shows that, over a time span of several days, the proportion of observations within 100 mm of the mean value is typically over 98% for the north and east components and 93% or better for the vertical component. Outliers exceeding 1 m are a small percentage (< 0.1%) of the observations, and automated algorithms will be required to reject them. Telemetry outages and the resulting baseline configuration change sometimes cause re-convergence to a different position. We expect that, with development of automated tools to handle outlier detection and configuration change, high-rate and real-time GPS results will significantly improve our capacity to monitor fault slip and respond to southern California earthquakes.